Package org.apache.flink.table.api.dataview

Class MapView<K,V>

java.lang.Object
org.apache.flink.table.api.dataview.MapView<K,V>
Type Parameters:
K - key type
V - value type
All Implemented Interfaces:
DataView
@PublicEvolving public class MapView<K,V> extends Object implements DataView
A DataView that provides Map-like functionality in the accumulator of an AggregateFunction or TableAggregateFunction when large amounts of data are expected.

A MapView can be backed by a Java HashMap or can leverage Flink's state backends depending on the context in which the aggregate function is used. In many unbounded data scenarios, the MapView delegates all calls to a MapState instead of the HashMap.

Note: Keys of a MapView must not be null. Nulls in values are supported. For heap-based state backends, hashCode/equals of the original (i.e. external) class are used. However, the serialization format will use internal data structures.

The DataTypes of the view's keys and values are reflectively extracted from the accumulator definition. This includes the generic argument K and V of this class. If reflective extraction is not successful, it is possible to use a DataTypeHint on top the accumulator field. It will be mapped to the underlying collection.

The following examples show how to specify an AggregateFunction with a MapView: 


 public class MyAccumulator {

   public MapView<String, Integer> map = new MapView<>();

   // or explicit:
   // {@literal @}DataTypeHint("MAP<STRING, INT>")
   // public MapView<String, Integer> map = new MapView<>();

   public long count;
 }

 public class MyAggregateFunction extends AggregateFunction<Long, MyAccumulator> {

  {@literal @}Override
  public MyAccumulator createAccumulator() {
    return new MyAccumulator();
  }

   public void accumulate(MyAccumulator accumulator, String id) {
     if (!accumulator.map.contains(id)) {
       accumulator.map.put(id, 1);
       accumulator.count++;
     }
   }

  {@literal @}Override
   public Long getValue(MyAccumulator accumulator) {
     return accumulator.count;
   }
 }

MapView(TypeInformation<?> keyType, TypeInformation<?> valueType) method was deprecated and removed. Please use a DataTypeHint instead.

  • Constructor Details

    • MapView

      public MapView()
      Creates a map view.

      The DataType of keys and values is reflectively extracted.

  • Method Details

    • getMap

      public Map<K,V> getMap()
      Returns the entire view's content as an instance of Map.

    • setMap

      public void setMap(Map<K,V> map)
      Replaces the entire view's content with the content of the given Map.

    • get

      public V get(K key) throws Exception
      Return the value for the specified key or null if the key is not in the map view.
      Parameters:
      key - The look up key.
      Returns:
      The value for the specified key.
      Throws:
      Exception - Thrown if the system cannot get data.

    • put

      public void put(K key, V value) throws Exception
      Inserts a value for the given key into the map view. If the map view already contains a value for the key, the existing value is overwritten.
      Parameters:
      key - The key for which the value is inserted.
      value - The value that is inserted for the key.
      Throws:
      Exception - Thrown if the system cannot put data.

    • putAll

      public void putAll(Map<K,V> map) throws Exception
      Inserts all mappings from the specified map to this map view.
      Parameters:
      map - The map whose entries are inserted into this map view.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • remove

      public void remove(K key) throws Exception
      Deletes the value for the given key.
      Parameters:
      key - The key for which the value is deleted.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • contains

      public boolean contains(K key) throws Exception
      Checks if the map view contains a value for a given key.
      Parameters:
      key - The key to check.
      Returns:
      True if there exists a value for the given key, false otherwise.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • entries

      public Iterable<Map.Entry<K,V>> entries() throws Exception
      Returns all entries of the map view.
      Returns:
      An iterable of all the key-value pairs in the map view.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • keys

      public Iterable<K> keys() throws Exception
      Returns all the keys in the map view.
      Returns:
      An iterable of all the keys in the map.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • values

      public Iterable<V> values() throws Exception
      Returns all the values in the map view.
      Returns:
      An iterable of all the values in the map.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • iterator

      public Iterator<Map.Entry<K,V>> iterator() throws Exception
      Returns an iterator over all entries of the map view.
      Returns:
      An iterator over all the mappings in the map.
      Throws:
      Exception - Thrown if the system cannot access the map.

    • isEmpty

      public boolean isEmpty() throws Exception
      Returns true if the map view contains no key-value mappings, otherwise false.
      Returns:
      True if the map view contains no key-value mappings, otherwise false.
      Throws:
      Exception - Thrown if the system cannot access the state.

    • clear

      public void clear()
      Removes all entries of this map.
      Specified by:
      clear in interface DataView

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • newMapViewDataType

      public static DataType newMapViewDataType(DataType keyDataType, DataType valueDataType)
      Utility method for creating a DataType of MapView explicitly.